Same as in Fig. 3, but this time the galaxies are grouped by their luminosity. The steel blue crosses indicate sub-LIRGs, the green filled circles LIRGs, and the red triangles ULIRGs. In the B-band, we also show the ULIRG sample with black asterisks that Lotz et al. (2004) used to define the merger region in the Gini-M₂₀ plane. Even though all ULIRGs in our sample are ongoing mergers, they do not appear to populate the corresponding part of the Gini-M₂₀ plane.